Sheet metal piston for transmissions and method of making a piston assembly

ABSTRACT

A multi-speed transmission with piston assemblies made from sheet metal stampings for selective engagement with multi-disc friction devices. Each piston assembly comprises a thin wall shell stamped from sheet stock. The shells have outer and inner support shoulders adjacent to outer and inner rims onto which are pressed annular retainers that form grooves for elastomeric lip seals. In one embodiment the contact member for the piston assembly comprises a sheet metal member curved until the ends almost meet. The contact member is retained in a shell by its expansion force acting against an annular retainer wall. In a second embodiment the contact member is formed by extending the outer rim axially.

United States Patent [1 1 Martin Oct. 28, 1975 [75] lnventor: James R.Martin, Ypsilanti, Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Sept. 4, 1973 [21] Appl. No.: 394,140

Related US. Application Data [62] Division of Ser. No. 288,905, Sept.14, 1972, Pat.

[52] US. Cl. 29/446; 29/DIG. 37; 29/450; 29/525 [51] Int. Cl. B231 11/02[58] Field of Search 29/156.5 R, 446, DIG. 37, 29/525, 450; 92/107, 108,130, 240, 255;

192/85 AA, 85 R 2,766,864 10/1956 Schilling et a1. 192/85 AA 2,815,99412/1957 Lippman et a1 3,120,156 2/1964 Ayers, Jr 92/108 3,321,056 5/1967Winchell et a1 192/85 R 3,338,584 8/1967 Nakanishi et al. 277/1863,370,682 2/1968 McFarland 192/85 AA 3,532,030 10/1970 Margetts 29/156.5R 3,541,887 11/1970 Van Lent et al..... 74/763 3,782,251 l/l974 Marchand92/130 Primary Examiner-C. W. Lanham Assistant Examiner-Dan C. CraneAttorney, Agent, or Firm-Charles R. White [5 7] ABSTRACT A multi-speedtransmission with piston assemblies made from sheet metal stampings forselective engagement with multi-disc friction devices. Each pistonassembly comprises a thin wall shell stamped from sheet stock. Theshells have outer and inner support shoulders adjacent to outer andinner rims onto which are pressed annular retainers that form groovesfor elastomeric lip seals. In one embodiment the contact member for thepiston assembly comprises a sheet metal member curved until the endsalmost meet. The contact member is retained in a shell by its expansionforce acting against an annular retainer wall. In a second embodimentthe contact member is formed by extending the outer rim axially.

2 Claims, 6 Drawing Figures U.S. Patent 0m. 28, 1975 Sheet 1 of2 2 I4 26w We '6?? 96 2.0 5%

US. Patent Oct. 28, 1975 Sheet 2 of2 3,914,849

SHEET METAL PISTON FOR TRANSMISSIONS AND METHOD OF MAKING A PISTONASSEMBLY This is a division of Ser. No. 288,905, filed Sept. 14, 1972,now US. Pat. No. 3,848,518.

This invention relates to hydraulically operated pistons fortransmissions and more particularly to a new and improved sheet metalpiston assembly and method for making such piston assemblies.

Many current transmissions incorporate clutch and brake-apply pistonsmachined from rough castings to close tolerances on most of theirsurfaces. This matching insures proper fit and proper operation of thepiston in the transmission. To reduce cost and weight, sheet metalpistons have been utilized in some transmission designs. Some of thesesheet metal pistons are disc-like diaphragms fixed at their centers to asupport and having a movable outer portion provided with an annularfriction surface for engagement with a clutch or brake pack. Other sheetmetal pistons mounted for unitary sliding movement in a bore drum orother support have been designed. However, these later pistons areincomplete assemblies without means to support and guide the pistonreturn spring and require bore mounted seals to establish pistonpressure chambers. Generally these pistons are complex in constructionand are not readily adaptable to currenttransmissions.

This invention "provides new and improved stamped sheet metal pistonsand a 'method of making such pistons. The piston has a shell-like bodystamped from sheet metal with inner and outer rims. Annular inner andouter shoulders are formed on one side of the shell onto which arepressed retainers with annular walls connected to have an L-shaped crosssection. In the installed position one wall makes annular contact withthe piston shell to space the other wall a predetermined distance fromthe shell to form annular grooves to provide seal ring retaininggrooves. An annular elastomeric lip seal is positioned in the inner andouter grooves to sealingly contact outer and inner walls of the pistonbore.

In addition to improved sealing the stamped piston has new and improvedprovision for supporting return springs used to move the piston to anoff position when pressure is relieved from the piston apply chamber. Ina first design a spring retainer having a circular arrangement ofaxially extending spring retaining tabs is welded or otherwise securedto the front face of the piston. A series of springs is mounted and heldon these tabs in the installed position. In a second design the face ofthe piston has an annular groove with offset and arcuately spaced springpockets formed therein. A plastic spring guide fits in the annulargroove and has a projection that fits in the pocket. With the projectionextending into the pocket, turning movement between the guide and thepiston shell is restricted. Openings formed in the projections of thespring guide permit passage of the springs therethrough and guide thesprings into seating engagement with a plate fixed to the membersupporting the piston.

In this invention there is new and improved construction for contactingthe multi-plate clutch or brake pack. In one embodiment a contact ringis stamped from a flat metal blank. This blank is provided withprojections extending from one side and curved into a spring-like memberwith the ends aligned and spaced a short distance from each other. Thisring member can be constricted and loaded into the piston and thenreleased so that its expansion force causes the projections to contactan annular wall in the face of the piston shell to releasably hold thering therein. This facilitates assembly and replacement of the ring ifneeded. In a second design the outer rim of the shell extends axiallyfrom the major portion of the shell to form the contact member.

These and other features, objects and advantages of this invention willbecome more apparent from the following detailed description anddrawings in which:

FIG. 1 is a side view of the transmission with the transmission coverbroken away in part;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is an exploded perspective view of the components of FIG. 2illustrating a first embodiment of the invention;

FIG. 4 is an enlarged side sectional view of a portion of FIG. 1 showinga second embodiment of the invention;

FIG. 5 is a sectional view taken generally along lines 5-5 of FIG. 1;and

FIG. 6 is an exploded perspective view of the components of FIG. 1 toillustrate a second embodiment of the invention.

The transmission of FIG. 1 has a three-element torque converter 10, acompound planetary gearset 12, two multiple disc clutches 14 and 16, amultiple-disc brake 18, two one-way brakes 20 and 22, and two bandbrakes 25 and 26. These clutches and brakes provide the frictionelements required to selectively condition the planetary gearset 12 forthree speeds forward and one speed reverse. The converter, gearing,brakes and clutches are substantially identical to correspondingelements disclosed in the US. Patent to Winchell et al, US. Pat. No.3,321,056 issued May 23, 1967 and operate in the same manner to providethree forward drives and one reverse drive.

Torque converter 10 has an engine driven pump 27, a turbine 28 and astator 30. Turbine 28 is drivingly connected to a turbine shaft 32 thatextends longitudinally along the rotational axis of the transmission.The end of the turbine shaft is splined to a first rotatable drum 34which houses clutch 14. As shown the drive plates of this clutch aresplined to the inner wall of drum 34 and the driven plates interleavedwith the drive plates are splined on the outer wall of a support 38which in turn is splined to one end of a longitudinally extendingintermediate shaft 40.

Multi-disc clutch 14 is engaged and released by a hydraulically operatedpiston assembly 42 mounted for longitudinal movement in drum 34. Thispiston assembly 42 comprises a thin-walled shell 44 stamped from sheetmetal with inner and outer annular rims 46 and 48. As best shown in FIG.3, the shell has an annular channel 50 in its face inwardly of outer rim48 to provide space for a convoluted clutch apply ring 52. An outerannular shoulder 56 having a diameter slightly less than the diameter ofouter rim 48 is formed on the back of the shell 44 onto which is pressfitted an annular lip seal retainer 58 also stamped from sheet metal. Asshown the retainer 58 has a longitudinally extending wall that contactsrim 48 to space a radially outwardly extending wall a predetermineddistance from rim 48 to provide an annular groove for an annularelastomer lip seal 60.

The piston shell 44 also is formed with an inner annular shoulder 64slightly greater than the inner diameter of rim 46 onto which is pressfitted an annular lip seal retainer 66 also stamped from sheet metal. Asshown the retainer 66 has a longitudinally extending wall that contactsrim 46 to space a radially extending wall a predetermined distance fromrim 46 to provide an annular groove for an annular elastomer lip seal68.

The outer and inner lip seals 60 and 68 provide sliding sealing contactwith the walls of a bore in the drum so that a pressure chamber isformed when the piston assembly is fitted therein. In the transmissionof FIG. 1 an intermediate annular lip seal 70 supported within drum 34contacts a cylindrical inner wall of the shell 44 to divide the pressurechamber into separate chambers so that clutch 14 can be engaged withhigh or low apply force.

A spring retainer 71, stamped from sheet metal, has a circular baseportion secured by projection welding or other suitable means to thefront face of the piston adjacent to inner rim 46. Retainer 71 has aseries of equally spaced tabs 72 which are arranged in a circle andwhich extend longitudinally from its base portion. Mounted on each ofthe tabs is a helical piston return spring 74. The far ends of springs74 are seated in an annular spring support 76 secured to the inner hubof drum 34. These springs provide the return force to move the pistonassembly to the off position when the pressure in the pressure chamberis exhausted.

The clutch apply ring 52 is made from a flat rectangular blank of sheetmetal. The rectangular blank is convoluted to provide arcuately spacedradial projections 80 and is then curled into a ring with free ends 82and 84 spaced a short distance from each other. The front and rear edgesof the ring are planar parallel surfaces. As best illustrated in FIGS. 2and 3, the apply ring is a cylindrical spring member that can be easilyconstricted and loaded into the piston shell. When the ring is released,the expansion force causes the radial projections 80 to contact anannular wall 86 in shell 44 forming the outer periphery of channel 50 tothus retain the ring in the piston shell. This construction facilitatesassembly or replacement of the contact ring in the piston shell.

Clutch 16 has driven plates splined to the inside of a second rotatabledrum 88 and drive plates splined to a cylindrical support 90 fixed tothe first drum 34. Drum 88 is splined at its hub to a sleeve shaft 91which is drivingly connected to the sun gears of planetary gearset 12. Asecond hydraulically actuated piston assembly 92 is disposed forlongitudinal movement in this drum to effect the engagement and releaseof clutch 16. This piston assembly is substantially the same as thefirst piston assembly 42 as shown by FIG. 1 and the detailed descriptionof piston assembly 42 applies to piston assembly 92. Drum 88 can be heldfrom rotation by band 26 or by multi-plate brake 18 and one way brake22.

Multi-plate brake 18 has first discs splined to the transmission caseinterleaved with second discs splined to the outer race of the one waybrake 22 which has its inner race fixed to drum 88. This brake isselectively engaged by a third piston assembly 96 to hold the outer raceof the one way brake 22 stationary so that it can engage to hold drum 88and the connected sun gears of the planetary gearset stationary tocondition the gearset for an intermediate drive range. This piston isstamped from metal sheet stock into an annular shell 98 with a centralopening to slidably fit in an annular bore or recess formed in a centersupport 100.

The shell 98 is formed with a forwardly extending outer cylindrical rim102 that has a planar contact face 104 for engaging the multiple discbrake 18. Press fitted on an outer cylindrical shoulder 106 formed onthe back of shell 98 is an annular lip seal retainer 108 stamped fromsheet metal. This retainer is similar to retainer 56 and cooperates withshell 98 to form an annular groove for an elastomer lip seal 110. Theshell 98 also has an annular radially extending inner rim 112 and anadjacent inner annular shoulder 114. An annular lip seal retainer 116similar to retainer 66 is press fitted on this shoulder and cooperateswith the inner rim 112 to form an annular groove for an elastomeric lipseal 118. The two lip seals establish pressure chamber 120 which whenfilled with pressure fluid causes the forward movement of the piston toengage the brake 18.

In the front face of shell 98 there is an annular channel 124 with threearcuately spaced spring pockets 126 for receiving a plastic spring guide128. The spring guide 128 has a flat ring-like base 130 that fits inchannel 124 and further has three offset projecting portions 132 thatfit in the spring pockets 126. The ends of these projecting portionscontact the end walls of the pockets to limit turning movement of theguide 128 relative to the shell 98. Each projecting portion of the guidehas two cylindrical openings 134 through which helical springs 136extend. As shown the spring 136 are seated in the spring pockets 126 andextend through the corresponding spring guide opening 134 intoengagementwith a support plate 140 that is secured toa shoulder of center support100. When pressure is relieved from the pressure chamber 120 the springswill move the piston back to the off position.

The compound planetary gear unit has a first gearset with an input ringgear 146 drivingly connected to the intermediate shaft 40. This ringgear meshes with planet gears 148 rotatably supported on carrier 150which is drivingly connected to the transmission output 152. Planetgears 148 mesh with sun gear 154 which in i turn is splined to the endof sleeve shaft 91 and which is drivingly connected to a sun gear 156 ofa second planetary set of the planetary unit. Sun gear 156 meshes withplanet gears 158 rotatably supported on a carrier 160 which is securedto a drum 161 and adapted to be held from rotation by one way brake 20or by reverse drive band brake 29. The ring gear 162 of this gearset isdrivingly connected to the output carrier 150.

The various brakes and clutches are applied as in the Winchell et alpatent identified above using the stamped sheet metal pistons of thisinvention instead of the cast and machined pistons and withoutalteration of the piston bores or other components of the transmissiondisclosed in that patent.

While preferred methods and embodiments of the invention have been shownand described in detail to illustrate the invention, various changes andmodifications may be made without departing from the scope of theinvention set forth in the following claims.

I claim:

1. A method of making a piston assembly for a friction driveestablishing device of a transmission comprising the steps of initiallystamping a thin-walled and cup-like shell of substantially uniformthickness from flat metal sheet stock, forming inner and outer annularrims integral with said shell, providing elastomeric seal means adjacentto said rims for hydraulically sealing said shell in a piston bore,forming an annular channel with a bottom wall and with inner and outerside walls in said shell concentric with said rims, stamping a flatrectangular blank of predetermined length and width from sheet metalstock, curving said blank into a partial circle with the free endsadjacent to each other to form a contact member for said friction driveestablishing device, constricting said contact member, loading saidconstricted contact member axially into said channel with the inneraxial edge thereof in contact with the bottom wall of said channel,releasing the contact member so that it radially expands into yieldingcontact with said outer side wall of said channel, and providing saidcontact member with a contact surface on the axially projecting endthereof for contact with said friction drive establishing device.

2. A method of making a sheet metal piston assembly for a frictiondrive-establishing device of a transmission comprising the steps ofstamping metallic sheet stock into a thin-walled annular shell withannular radially extending outer and inner rims, forming a firstcylindrical shoulder on said shell adjacent to said outer annular rimwith a diameter slightly less than the outside diameter of said outerannular rim, forming a second cylindrical shoulder on said shelladjacent to said inner annular rim with a diameter slightly greater thanthe inside diameter of said inner annular rim, securing an annularretainer with a radially extending flange on said first cylindricalshoulder spaced a predetermined distance from said outer rim to form anouter annular channel therebetween, installing an annular elastomericlip seal having an outer diameter slightly greater than the outerdiameter of said outer rim in said channel, securing an annular retainerwith a radially extending flange on said second annular shoulder spaceda predetermined distance from said inner rim to form an inner annularchannel therebetween, installing an annular elastomeric lip seal havingan inner diameter slightly less than the inner diameter of said innerrim in said last mentioned channel, stamping a flat rectangular blankfrom sheet metal sheet stock, curling said sheet metal stock into acircular spring having free end portions adjacent to each other, saidspring forming a contact member for the friction drive establishingdevice of the transmission, constricting said contact member, insertingsaid constricted contact member axially into said shell, releasing saidcontact member from the constricting force so that it expands intoyielding contact with an inner wall portion of said first cylindricalshoulder and so that the projecting end face thereof provides a contactsurface for the friction drive establishing device of the transmission,providing a ring of spaced sheet metal projections on the inner face ofsaid shell adjacent to an inner wall portion of said second cylindricalshoulder for retaining piston return springs

1. A method of making a piston assembly for a friction driveestablishing device of a transmission comprising the steps of initiallystamping a thin-walled and cup-like shell of substantially uniformthickness from flat metal sheet stock, forming inner and outer annularrims integral with said shell, providing elastomeric seal means adjacentto said rims for hydraulically sealing said shell in a piston bore,forming an annular channel with a bottom wall and with inner and outerside walls in said shell concentric with said rims, stamping a flatrectangular blank of predetermined length and width from sheet metalstock, curving said blank into a partial circle with tHe free endsadjacent to each other to form a contact member for said friction driveestablishing device, constricting said contact member, loading saidconstricted contact member axially into said channel with the inneraxial edge thereof in contact with the bottom wall of said channel,releasing the contact member so that it radially expands into yieldingcontact with said outer side wall of said channel, and providing saidcontact member with a contact surface on the axially projecting endthereof for contact with said friction drive establishing device.
 2. Amethod of making a sheet metal piston assembly for a frictiondrive-establishing device of a transmission comprising the steps ofstamping metallic sheet stock into a thin-walled annular shell withannular radially extending outer and inner rims, forming a firstcylindrical shoulder on said shell adjacent to said outer annular rimwith a diameter slightly less than the outside diameter of said outerannular rim, forming a second cylindrical shoulder on said shelladjacent to said inner annular rim with a diameter slightly greater thanthe inside diameter of said inner annular rim, securing an annularretainer with a radially extending flange on said first cylindricalshoulder spaced a predetermined distance from said outer rim to form anouter annular channel therebetween, installing an annular elastomericlip seal having an outer diameter slightly greater than the outerdiameter of said outer rim in said channel, securing an annular retainerwith a radially extending flange on said second annular shoulder spaceda predetermined distance from said inner rim to form an inner annularchannel therebetween, installing an annular elastomeric lip seal havingan inner diameter slightly less than the inner diameter of said innerrim in said last mentioned channel, stamping a flat rectangular blankfrom sheet metal sheet stock, curling said sheet metal stock into acircular spring having free end portions adjacent to each other, saidspring forming a contact member for the friction drive establishingdevice of the transmission, constricting said contact member, insertingsaid constricted contact member axially into said shell, releasing saidcontact member from the constricting force so that it expands intoyielding contact with an inner wall portion of said first cylindricalshoulder and so that the projecting end face thereof provides a contactsurface for the friction drive establishing device of the transmission,providing a ring of spaced sheet metal projections on the inner face ofsaid shell adjacent to an inner wall portion of said second cylindricalshoulder for retaining piston return springs thereon.